1. Field of the Invention
This invention relates to a multi-layered magneto-resistance effect film having repeatedly layered magnetic and non-magnetic layers and which exhibits a giant magneto-resistance effect. This invention also relates to a magneto-resistance effect device employing this multi-layered magneto-resistance effect film and to a magneto-resistance effect magnetic head employing this magneto-resistance effect device.
2. Description of the Related Art
The magneto-resistance effect device is a device used for detecting a magnetic field and usually includes a substantially rectangular magneto-resistance effect film and a pair of electrodes mounted on both longitudinal ends of the magneto-resistance effect film. The magneto-resistance effect film is a thin film the resistance value of which is changed with the magnitude of the external magnetic field. For detecting the external magnetic field using the magneto-resistance effect device, a constant sense current is usually supplied via a pair of electrodes to the magneto-resistance effect film for detecting changes in voltage of the sense current. Specifically, with the magneto-resistance effect device, the magneto-resistance effect film is changed in resistance with changes in the external magnetic field, this change in resistance being detected as changes in voltage of the sense current.
This magneto-resistance effect device is used in, for example, a playback magnetic head. The playback magnetic head employing the magneto-resistance effect device is termed a magneto-resistance effect magnetic head and detects the signal magnetic field from a recording medium as resistance changes of the magneto-resistance effect device.
As such magneto-resistance effect device, such device employing an NiFe alloy film (so-called permalloy film) exhibiting the anisotropic magneto-resistance effect as a magneto-resistance effect film has been extensively used. However, the magneto-resistance effect device employing the permalloy film is low in magneto-resistance change rate and hence a magneto-resistance effect device exhibiting higher magneto-resistance change rate has been desired.
In particular, the magneto-resistance change rate of the magneto-resistance effect device employing the permalloy film is as low as approximately 2% or less under conditions in which the device is used in a magnetic head. Thus, with the tendency to increased density in magnetic recording, a magneto-resistance effect device exhibiting stronger magneto-resistance effect has strongly been desired as a magneto-resistance effect device used for a magneto-resistance effect magnetic head.
It has recently been reported that an extremely high magneto-resistance effect, or so-called giant magneto-resistance effect, can be achieved with a multi-layered film of an artificial lattice film structure made up of layers each being of a thickness of plural atoms of different sorts of metals or the like layered together. Specifically, in M. N. Baibich et al, "Phys. Rev. Lett. 61, p.2472 (1988), it is reported that a multi-layered film of an artificial film structure made up of magnetic layers of Fe and non-magnetic layers of Cr layered together exhibits the giant magneto-resistance effect. Also, in S. S. P. Parkin et all. "Phys. Rev. Lett. 66, p2152 (1991), it is reported that a giant magneto-resistance effect can be achieved with a multi-layered film of an artificial lattice film structure made up of magnetic layers of Co and non-magnetic layers of Cu layered together.
It is felt that the reason the giant magneto-resistance effect can be realized with the multi-layered film of the artificial lattice structure is that Rudermann-Kittel-Kasuya-Yoshida (RKKY) interaction operates between the magnetic layers via conduction electrons in the non-magnetic layers and the opposing magnetic layers are anti-ferromagnetically coupled together to produce anti-parallel spin state to give rise to spin-dependent scattering.
Since the magneto-resistance effect film made up of plural layers of the artificial lattice film structure, referred to herein as a multi-layered magneto-resistance effect film, exhibits a magneto-resistance effect far stronger than the magneto-resistance effect exhibited by the permalloy film, the application thereof to magneto-resistance effect devices or to magneto-resistance effect magnetic heads is thought to be promising.
The multi-layered magneto-resistance effect film has, however, a drawback that, while it has a large rate of change of resistance values, it needs a significant change in magnetic field for realization of a change in resistance. That is, the multi-layered magneto-resistance effect film is insufficient in sensitivity such that it cannot be used in a device in need of detecting a low magnetic field intensity such as a magnetic head. Thus, for using the multi-layered magneto-resistance effect film in a device in need of detecting a low magnetic field intensity, such as a magnetic head, it becomes necessary to render it possible to achieve a large change in resistance even for a small change in magnetic field.
Referring to FIG. 1, such multi-layered magneto-resistance effect film 100 is substantially rectangular in shape and is of a pattern made up of magnetic layers 101 of a magnetic material exhibiting soft magnetic properties and non-magnetic electrically conductive layers 102 layered together repeatedly. With the multi-layered magneto-resistance effect film 100, the magnetic layers 101, layered to one another with interposition of the non-magnetic electrically conductive layers 102, are magnetized so that the respective directions of magnetization run anti-parallel to one another, that is, the magnetic layers 101 are layered in parallel with alternate magnetic layers 101 exhibiting opposite directions of magnetization.
For detecting the external magnetic field in such multi-layered magneto-resistance effect film 100, the sense current is supplied along its length as indicated by arrow S in FIG. 1. With the multi-layered magneto-resistance effect film 100, the resistance value relative to the sense current becomes maximum if the direction of magnetization of the neighboring magnetic layers 101 is anti-parallel to one another, as stated above. If the external magnetic field is impressed across the multi-layered magneto-resistance effect film 100 with the directions of magnetization of the neighboring magnetic layers being parallel to each other, the resistance value to the sense current becomes minimum.
The magneto-resistance effect device, employing the above-described multi-layered magneto-resistance effect film 100 as a magnetically sensitive portion, is used for a magneto-resistance effect magnetic head for detecting the signal magnetic field emanating from the magnetic recording medium. This magneto-resistance effect magnetic head detects changes in resistance with respect to the sense current by the signal magnetic field as changes in voltage for reproducing the signal magnetic field.
If the sense current of large current value is supplied to the above-described multi-layered magneto-resistance effect film 100, there is generated a sense current magnetic field of a magnitude proportionate to the current value. This sense current magnetic field is an annular magnetic field substantially centered at the center of current density distribution, that is an annular magnetic field indicated by arrow T in FIG. 2.
In the multi-layered magneto-resistance effect film 100, the direction of magnetization of the magnetic layers 101, layered with the non-magnetic electrically conductive layers in-between, is changed with this sense current magnetic field, as shown in FIG. 2. That is, the sense current magnetic field destructs the weak anti-ferromagnetic coupling formed between neighboring are aligned in one direction in which these magnetic layers 101 become anti-parallel to one another with substantially the center along the film thickness of the magnetic layer 101 as a boundary.
Thus, with the multi-layered magneto-resistance effect film 100, the direction of magnetization of the magnetic layers 101 becomes anti-parallel only near the center in the direction along the film thickness thereof while becoming substantially parallel in the remaining portions. The result is that, with the multi-layered magneto-resistance effect film 100, spin-dependent scattering occurs only in the vicinity of the center along the film thickness, while no magneto-resistance effect is displayed in the remaining portions. Thus, with the multi-layered magneto-resistance effect film 100, the amount of change in resistance value with respect to the external magnetic field becomes smaller since the large sense current is supplied to generate a large sense current magnetic field. That is, the multi-layered magneto-resistance effect film 100 has a drawback that, even if the sense current is increased for improving the detection sensitivity of the magneto-resistance effect, the detection sensitivity cannot be improved as desired.
Moreover, if the magneto-resistance effect device employing the multi-layered magneto-resistance effect film 100 is used as the magneto-resistance effect type magnetic head, detection sensitivity to the external magnetic field is deteriorated by the sense current magnetic field, as described above. The result is that this magneto-resistance effect type magnetic head is deteriorated in reproduction sensitivity in reproducing the signal magnetic field of the magnetic recording medium.